The present invention relates to a hydraulically controlled disk brake of a motor vehicle having at least one hydraulically actuable brake piston that is arranged in a caliper and is guided in at least one cylinder. Published Examined patent application No. 1,284,724 which comprises brake pistons that are arranged in a caliper and are guided in cylinders. The cylinders of the brake pistons are connected with one another via a ring duct. This disk brake is equipped with two brake pistons that are located opposite to one another in the caliper, and the connecting ring duct is constructed so that a joint inlet and outlet opening is created that is arranged centrically with respect to a piston. Via the check valves that are each arranged in the ring duct in the area of the connection of the two U-shaped caliper halves so that they are offset by 90.degree. with respect to the piston, a supplying and removing of brake fluid takes place when the disk brake is actuated. In this type of design, when the brake is released, only an insufficient exchange of brake fluid is possible within the caliper because an exchange takes place mainly within the duct between the cover and flange side of the caliper. When the brake is released, a part of the ejected brake fluid of the rear brake cylinder in the inner ring duct is carried along to the outlet opening, whereas another part remains in the area of the front brake cylinder so that, during a braking process that follows, the same, only slightly cooled brake fluid will act upon the pistons. In this disk brake, therefore, no complete exchange of brake fluid takes place, particularly no exchange of the brake fluid of the rear cylinder that exists away from the outlet opening, and thus also no effective cooling can take place.
It is an objective of the present invention to provide a disk brake with such a circulation and exchange of brake fluid when the brakes are actuated that excessive heating and thus a gas formation is avoided.
These and other objectives are achieved in a hydraulically controlled disk brake having a plurality of hydraulically actuable brake pistons that are arranged in a caliper and are guided in respective cylinders, by providing duct means for continuously serially connecting the cylinders in each half of the caliper, these duct means having separate outlet and inlet openings. The check valves for each inlet and outlet opening are respectively arranged in front of the first cylinder after the inlet opening and behind the last cylinder before the outlet opening with respect to flow direction.
The main advantages that are achieved by means of the invention are that a complete circulation of fluid takes place, and the fluid that is heated during the braking in the spaces of the cylinders is exchanged so that a formation of gas bubbles is counteracted.
In particular, the inner duct that connects the cylinders behind one another has an outlet opening that is separate from the inlet opening so that already at this point, a physical separation takes place of warm and cold brake fluid. In addition, the duct is designed in such a way that the volume of the brake fluid that is present in the cylinders during braking, when the brake is released, is pushed out completely via the outlet opening, and when braking takes place again, only cold brake fluid can be fed to the duct via the inlet opening.
The directly adjacent assignment of the openings to the respective cylinders in the caliper has the advantage of a short duct length, and thus a fast exchange of the fluid is ensured. An optimized supplying and removing of brake fluid into and out of the cylinder spaces is promoted by the duct inlet and outlet into the area of the largest cross-section of the cylinder, in certain preferred embodiments.
In certain preferred embodiments, the outlet pipe that branches off the supply pipe, is located with its mouth in front of the inlet check valve as seen in flow direction of the brake fluid during braking, and provides the possibility of an admixing of the ejected heated brake fluid to the newly supplied cold brake fluid.
An opposed flow direction through the cylinders of each side is provided in certain preferred embodiments, although other embodiments have the same flow direction through the cylinders. In those embodiments, improved ventilating conditions must be provided.
The duct in the caliper may have an inlet opening that is located at any arbitrary point. For example, in certain preferred embodiments, the inlet opening is arranged between the cylinders of one half of the caliper. In certain further preferred embodiments, the valves are arranged rigidly outside the caliper or also inside the caliper.
Although in the drawings, disk brakes are shown that each have two pistons in each half, the duct design and its guiding can also be used for disk brakes with less than two pistons and more than two pistons per half of the caliper.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.